LeetCode Solutions : Remove Duplicates from Sorted List I & II

Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,

Given 1->1->2, return 1->2.

Given 1->1->2->3->3, return 1->2->3.

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) {
*         val = x;
*         next = null;
*     }
* }
*/
public class Solution {
public ListNode deleteDuplicates(ListNode head) {
if(head==null||head.next==null)
return head;
ListNode visited=head;
while(visited!=null&&visited.next!=null){
if(visited.val==visited.next.val)
visited.next=visited.next.next;
else
visited=visited.next;
}
return head;
}
}

Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,

Given 1->2->3->3->4->4->5, return 1->2->5.

Given 1->1->1->2->3, return 2->3.

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) {
*         val = x;
*         next = null;
*     }
* }
*/
public class Solution {
public ListNode deleteDuplicates(ListNode head) {
if(head==null||head.next==null)
return head;
ListNode pre=new ListNode(0);
pre.next=head;
head=pre;
while(pre.next!=null){
ListNode cur=pre.next;
while(cur.next!=null&&cur.next.val==cur.val)
cur=cur.next;
if(pre.next==cur){ // don't find the duplicate
pre=pre.next;
}else{ //remove the duplicate node
pre.next=cur.next;
}
}
return head.next;
}
}